A. Mobile Communication System
First, referring to FIG. 1, a brief description will be given of a mobile communication system in 3GPP (3rd Generation Partnership Project). Note that nodes and functions that do not relate to the background art of the present invention will be omitted.
As shown in FIG. 1, the mobile communication system is comprised broadly of several networks including a core network 10, an access network 20, an external IP (Internet Protocol) network 30, and the Internet 40, and a mobile terminal 50 connected to the access network 20 in a mobile manner.
The mobile terminal 50 can use services provided from the external IP network 30 and the Internet 40, through the access network 20 and the core network 10. Here, although the external IP network 30 and the Internet 40 are identical in the point that they are both IP networks, they are distinguished from each other for the sake of convenience.
The core network 10 is a network managed by an operator that mainly provides mobile communication services and is assumed to be Evolved Packet Core (EPC) here. The core network 10 includes a packet network GW 100, an access network GW 200, a HSS (Home Subscriber Server) 400, a MME (Mobility Management Entity) 300, and a local GW 500.
Here, the packet GW network 100 corresponds to a packet data network gateway (PDN GW) or GGSN (Gateway GPRS (General Packet Radio Service) Support Node) in 3GPP. Moreover, the access network GW 200 corresponds to a serving gateway (S-GW) or SGSN (Serving GPRS Support Node).
The packet network GW 100 has a function as an anchor which transfers communication data addressed to the mobile terminal 50 to the mobile terminal 50 when the mobile terminal 50 has moved within the access network 20 where the same radio technology is applied, or has moved between the access networks 20 where different radio technologies are applied. Moreover, the packet network GW 100 has a role as a gateway to the external IP network 30.
The access network GW 200 has a role as a gateway which provides a function of connecting to the access network 20, and has a function of transferring user data transmitted from a radio base station 600, which is originated from the mobile terminal 50, to the packet network GW 100. The access network GW 200 has a function of, reversely, transferring user data transmitted from the packet network GW 100, which is addressed to the mobile terminal 50, to the radio base station 600. Moreover, the access network GW 200 also has a function as an anchor when the mobile terminal 50 has moved within a range the access network GW 200 covers in the access network 20.
The MME 300 has a function of setting and managing a data path in accordance with a policy of the network (i.e., a policy of the operator operating the network) and with a request from the mobile terminal 50. When the mobile terminal 50 has connected to the mobile communication system, the MME 300 downloads from the HSS 400 various setting information associated with a subscriber of this mobile terminal 50 and executes setting and management of a data path based on the information obtained here. Here, the data path is a logical data path set up between the packet network GW 100 and the mobile terminal 50 via the access network GW 200 and the radio base station 600, and user data for the mobile terminal 50 is transferred through this data path. This logical data path is called bearer and is assigned a bearer identifier that, with identification information on the mobile terminal, uniquely identifies the bearer. Moreover, a unit formed by collecting a plurality of bearers between the mobile terminal 50 of interest and the packet network GW 100 is called PDN connection. The MME 300 is a node that processes control signals, and one of the features of EPC is an architecture in which such control signal processing and user data processing are split. Such an architecture is called C (Control)-plane/U (User)-plane split.
The HSS 400 maintains subscriber information and has a function of performing processing for authenticating the mobile terminal 50 and, by request from the MME 300, transmitting to the MME 300 various setting information associated with the mobile terminal 50 as mentioned above.
The access network 20 is a network that accommodates mobile terminals based on a radio access technology such as LTE (Long Term Evolution), W-CDMA (Wideband Code Division Multiple Access), or WLAN (Wireless Local Area Network). The radio base station 600 is deployed in the access network 20, and the radio base station 600 connects to the mobile terminal 50 by using the radio access technology. The radio base station 600 corresponds to eNodeB, or a set of RNC (Radio Network Controller) and NodeB in 3GPP.
The external IP network 30 is an IP network connected to the core network 10 via the packet network GW 100, and various servers and the like placed in this network provide services to the mobile terminal 50. For example, in some cases, the external network 30 is a network managed by the same manager that manages the core network 10; in other cases, it is a network managed by a different fixed IPS (Internet Service Provider) or a network of an enterprise.
The mobile terminal 50 includes a radio interface and connects to the radio base station 600 by using a radio access technology. The mobile terminal 50, upon connecting to the radio base station 600, can access services provided in the external IP network 30 and the Internet 40 by using a user data transmission path (i.e., bearer) set up between the packet network GW 100 and the mobile terminal 50. The mobile terminal 50 corresponds to UE (User Equipment) in 3GPP.
Incidentally, to avoid complicating the drawing, FIG. 1 shows a single packet network GW 100, a signal access network GW 200, and a single radio base station 600. However, an actual topology is a tree topology in which a packet network GW 100 is at the top and a plurality of radio base stations 600 are at the lowest ends, that is, a packet network GW 100 accommodates a plurality of access network GWs 200, and each access network GW 200 further accommodates a plurality of radio base stations 600. With such a structure, it is possible to provide continual communication services even when the mobile terminal 50 moves between radio base stations.
B. Relocation
In recent years, there are increasing opportunities when moving images are viewed on mobile telephones. This trend is growing stronger due to the advent of smart phones typified by iPhone (registered trademark) and Android (registered trademark). Moreover, it is expected that traffic for view of moving images will experience explosive growth in future, due to higher-resolution terminals, enhanced processing performance, and LTE-based broader wireless bandwidth.
An existing mobile communication system is in a tree topology with an anchor, which is the packet network GW 100, placed at the top, as described earlier. Therefore, it is conceivable that traffic is concentrated on the packet network GW 100, which will be incapable of handling an explosive increase in traffic in future. Although it is possible to distribute the loads by increasing the number of packet network GWs 100, there is a problem that excessive costs incur. Moreover, the fact will not be changed that large amounts of network resources in the core network 10 are consumed.
To solve this problem, in 3GPP, a technique is proposed and approved in which specific traffic such as traffic of a moving image is bypassed to the external IP network 30 from a location as close as possible to the access network 20. This is the technique called SIPTO (Selected Internet Protocol Traffic Offload) (for example, see NPL 1, page 33, 4.3.15).
According to SIPTO, basically, a set of the packet network GW 100 and the access network GW 200 is placed close to the access network, and such a structure is almost similar to the above-described structure. However, an actual product is expected to be smaller in size and lower in performance and cost than the packet network GW100 and the access network GW 200. Moreover, such a packet network GW 100 and an access network GW 200 are expected to be co-located in a single box. In this case, it is conceivable that in some cases, the packet network GW and the access network GW are mounted on different respective blades, which are installed on a single chassis; in other cases, respective software of the packet network GW and the access network GW individually operates on the same blade. Further, in other conceivable cases, respective functions of the packet network GW and the access network GW are executed by using the same software in some cases. Various methods are conceivable for such a co-location method.
The local GW 500 in FIG. 1 is a node in which a packet network GW 100 and an access network GW 200 as described above are co-located. The local GW 500 is connected to an external IP network 30b through a function of the internal packet network GW, and also functions as an anchor when the mobile terminal 50 has moved. Moreover, similarly to the access network GW 200, the local GW 500 also has interfaces with the MME 300 and the radio base station 600. Note that a conceivable example of the external IP network 30b is a network of a fixed network carrier that provides IP connection services near the local GW 500.
Loads on the core network 10 can be reduced by placing the local GW 500 near the radio base station 600. However, when the mobile terminal 50 has moved greatly, there are some cases where there is another local GW 500 that is closer to a radio base station 600 to which the mobile terminal 50 has moved to. In this case, it is preferable to change (relocate) the local GW 500 for accommodating the mobile terminal 50 to a local GW 500 that is more suitable, i.e., closer geographically or network-topologically.
For this relocation processing, a “MME requested PDN disconnection” procedure (NPL 1, FIG. 5.10.3-1) shown in FIG. 2 or a “MME-initiated Detach” procedure (NPL 1, FIG. 5.3.8.3-1) shown in FIG. 3 is applied. Although details thereof are omitted, in the MME requested PDN disconnection procedure, a PDN connection serving as a user data transmission path set up between a packet network GW (PDN-GW) and a mobile terminal (UE) is disconnected, and in the MME-initiated Detach procedure, a mobile terminal is once disconnected from a network. Then, in any of the procedures, a signal containing information for requesting re-connection is transmitted to the mobile terminal 50.
Specifically, in the MME requested PDN disconnection procedure shown in FIG. 2, information for requesting to reconfigure a PDN connection is contained in Step 7 (Deactivate Bearer Request). In the MME-initiated Detach procedure shown in FIG. 3, information for requesting re-connection is contained in Step 1(Detach Request). As a result, the mobile terminal 50 performs processing for re-connecting to a new PDN-GW and, upon this re-connection, is newly assigned a PDN-GW that is closer to it. Since the local GW 500 is a node in which a PDN-GW and a S-GW are co-located as described above, relocation can be achieved through similar processing. Hereinafter, unless otherwise noted, packet network GW (P-GW) relocation will also include local GW relocation.
As described above, relocation of the packet network GW 100 in SIPTO is performed through the procedure shown in FIG. 2 or 3 by the MME 300, with a policy of the network taken into consideration.
Regarding processing for access network GW relocation, PTL 1 discloses a method for determining relocation execution timing. For an access network GW disclosed in PTL 1, relocation following a change in communication path at the time of handover is performed if the total data throughput per unit time of a relocation-target access network GW is smaller than a predetermined value. That is, relocation is performed when loads on a relocation target is small, whereby the rate of success is increased.